How was bacterial transformation proved experimentally? Who has performed this experiment?

Question of 96

Q. How was bacterial transformation proved experimentally? Who has performed this experiment?

Jharkhand JacJAC Intermediate Board 2025Subjective· 5mImportance★★★★★

0% · 0/96 Questions

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Frederick Griffith's 1928 experiment with Streptococcus pneumoniae in mice first demonstrated bacterial transformation, and Avery, MacLeod, and McCarty's 1944 experiment identified DNA as the 'transforming principle' responsible for it.

Griffith's experiment (1928): Griffith worked with two strains of the bacterium Streptococcus pneumoniae - the S (smooth) strain, which has a polysaccharide coat, is virulent (disease-causing), and kills mice; and the R (rough) strain, which lacks the coat, is non-virulent, and does not kill mice. Griffith performed four sets of injections into mice:

Live S strain -> mice died.
Live R strain -> mice survived.
Heat-killed S strain -> mice survived.
Heat-killed S strain mixed with live R strain -> mice died, and live S-strain bacteria were recovered from their blood.

Since neither the heat-killed S strain nor the live R strain alone could kill the mice, but their combination did, Griffith concluded that some 'transforming principle' had been transferred from the dead S bacteria into the live R bacteria, genetically converting (transforming) some of the R bacteria into the virulent S form - a heritable change. However, Griffith's experiment did not identify the chemical nature of this transforming principle.

…

Start your 14-day free trial to unlock the full solution →

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set SEM31 markMCQ
$Q. Read the following passage below and answer next four questions (23 - 26) related to it : In his experiment Griffith isolated two strains of bacteria, one was rough walled with pili on the wall and the other one covered with an extremely slimy coat hence smooth in nature. He injected type II R to mice and the mice could survive. Type III S was injected to mice and it died of Pneumonia. Heat killed (HK) strains of the same (Type III S) when injected to the mice, it was alive or did not die. But when the mice was injected with III S (HK) and II R mixed the mice was found to be dead and virulent III S were recovered from the dead remains of the mice. [Q23] Name the process which is observed in this experiment :$
(a) Bacterial transduction
(b) Bacterial transformation
(c) Bacterial conjugation
(d) Bacterial transfection
›Reveal solutionSolution
In Griffith's 1928 experiment, live avirulent R bacteria mixed with heat-killed virulent S bacteria killed the mice and yielded live S bacteria. The R bacteria were genetically 'transformed' by material from the dead S cells — the process of bacterial transformation.

Griffith worked with Streptococcus (Diplococcus) pneumoniae:

Live S (smooth, virulent) → mice die.

Live R (rough, avirulent) → mice live.

Heat-killed S → mice live.

Heat-killed S + live R → mice die, and live S are recovered. …
Start your 14-day free trial to see the full solution →
CBSE 2026Set SEM31 markMCQ
$Q. Which bacteria was used in this famous experiment by Griffith ?$
(a) Diplococcus pneumoniae
(b) Bacillus subtilis
(c) Haemophilus influenzae
(d) E. coli
›Reveal solutionSolution

Griffith performed his transformation experiment on the bacterium Streptococcus pneumoniae, historically called Diplococcus pneumoniae, which causes pneumonia in mammals.

The bacterium used by Frederick Griffith (1928) was Streptococcus pneumoniae (older name Diplococcus pneumoniae), the causative agent of pneumonia. It occurs as two strains: the virulent S (smooth, capsulated) type and the avirulent R (rough, non-capsulated) type. The other options — Bacillus subtilis, *Haemoph …

Start your 14-day free trial to see the full solution →
CBSE 2026Set SEM31 markMCQ
$Q. Which of the following statements is incorrect about HK III (S) ?$
(a) Heat killed III S strain was rough in nature
(b) Avirulent
(c) Heat killed III S strain was smooth in nature
(d) Type III S bacterial strain was heated at high temperature to make the heat killed strain HK III S
›Reveal solutionSolution
The type III S strain is smooth (S = smooth, capsulated); heating only kills it, it does not change its smooth wall to rough. So saying HK III S was 'rough in nature' is incorrect.

Evaluating each statement about heat-killed (HK) type III S:

(a) "Heat killed III S strain was rough in nature" — INCORRECT. The S strain is smooth (has a mucous/polysaccharide capsule); heat kills the cells but does not convert its smooth wall into a rough one.

(b) "Avirulent" — correct; once heat-killed, the S cells cannot cause disease.

(c) "Heat killed III S strain was smooth in nature" — correct; it retains its smooth (capsulated) character. …
Start your 14-day free trial to see the full solution →
CBSE 2026Set SEM31 markMCQ
$Q. Why do HK III S + II R when administered together, they become deadly ?$
(a) III S remain unchanged
(b) II R remain avirulent
(c) The avirulent II R changed to type III S
(d) The HK III S changed to type II R and got virulent
›Reveal solutionSolution

When HK III S and live II R are given together, the transforming principle (DNA) from the heat-killed S enters the living R cells and transforms them into virulent S bacteria — so the mixture becomes deadly.

Heat-killed III S alone is harmless, and live II R alone is harmless. But together, genetic material (the 'transforming principle', later identified as DNA) released from the dead S cells is taken up by the living R cells. This converts (transforms) the avirulent II R into virulent III S bacteria, which multiply, cause pneumonia, and kill the mice — and virulent S can be recovered from the dead mice.

…

Start your 14-day free trial to see the full solution →
CBSE 2024Set A11 markMCQ
$Q. In Griffith's experiment, mice infected with the A die from pneumonia infection, but mice infected with B don't develop pneumonia.$
(a) A → S-Strain; B → S-Strain
(b) A → S-Strain; B → R-Strain
(c) A → R-Strain; B → S-Strain
(d) A → R-Strain; B → R-Strain
›Reveal solutionSolution

In Griffith's experiment the virulent S-strain kills mice, while the non-virulent R-strain does not.

Frederick Griffith worked with Streptococcus pneumoniae. The smooth (S) strain has a mucous (polysaccharide) capsule, is virulent, and mice infected with it die of pneumonia. The rough (R) strain lacks the capsule, is non-virulent, and mice inf …
Start your 14-day free trial to see the full solution →

←Previous chapterCh 4Principles of Inheritance and Variation

Q.How was bacterial transformation proved experimentally? Who has performed this experiment?

Concept understanding — Griffith's Transformation Experiment

Q.How was bacterial transformation proved experimentally? Who has performed this experiment?

🎓Unlock everything free for 14 days

Unlock everything free for 14 days